You arrive on scene in an apartment to find a 25-year-old female who’s unresponsive and apneic in the bathroom by her roommate, covered in vomitus and surrounded by empty medication containers and a bottle of tequila.

The patient’s roommate notes that the patient has a history of depression and drug abuse, takes “some medication every night,” and that the patient had been crying all day after her boyfriend broke up with her.

Naloxone was administered by police with no effect, and the patient fails to breathe adequately on her own despite airway repositioning and suctioning.

You quickly decide this patient requires intubation for airway protection. You’re deciding which medications to give the patient. You decide ketamine and succinylcholine … No—wait—ketamine and rocuronium …

Rapid Sequence Intubation

Rapid sequence intubation (RSI) is a particular type of endotracheal intubation that aims to quickly and effectively induce sedation and paralysis in a patient who’s at high risk for aspiration or impending airway compromise.

RSI was first described by Stept and Safar in 1970 and was initially called “rapid sequence induction and intubation.” RSI was created as a response to the deleterious effects of aspiration that were first described by Mendelson in 1946. The purpose of this technique was to decrease the amount of time that a patient’s airway was unprotected during induction.1

RSI is widely considered the safest and preferred method to intubate a critical patient who’s at increased risk for pulmonary aspiration or airway compromise in order to increase the chance of first-pass success and visualize the vocal cords.

In general, RSl is performed by first administering a sedative, followed rapidly by a paralytic, before an attempt is made to intubate. There has been much debate over which type of neuromuscular blockade should be used to paralyze patients during RSI, and many EMS systems only offer RSI with one particular medication over the other, and have been exclusively taught on one first-line medication. Many providers choose their preferred paralytic based on side effect profile, length of action and experience.

So, without further ado, let’s meet our contenders!

Succinylcholine (Anectine)

Succinylcholine was first discovered in 1906 by Reid Hunt and René de M. Taveau. When studying the drug, animals were given curare—a poisonous plant extract that paralyzes the motor nerves—and studied the neuromuscular blocking properties of succinylcholine. In 1949, an Italian group led by Daniel Bovet was first to describe succinylcholine-induced paralysis. The clinical introduction of succinylcholine was described in 1951 by several groups.2

The pharamacokinetics of succinylcholine make it the classic depolarizing muscle relaxant, since it’s an analogue of acetylcholine (ACh), it stimulates all cholinergic receptors throughout the parasympathetic and sympathetic nervous systems. Succinylcholine binds directly to the postsynaptic ACh receptors of the motor endplate, causing continuous stimulation of these receptors. This leads to transient fasciculations followed by muscular paralysis.

Succinylcholine is often dosed at 1.0–1.5 mg/kg. It’s considered a rapid onset, one circulation time, quick-offset medication with an onset of 45–60 seconds, and a duration of action of 4–6 minutes of paralysis. Its metabolism and half-life is unknown.3

Rocuronium (Zemuron)

Rocuronium was first introduced in 1994 as a better, less tachycardiac and histamine releasing alternative to pancuronium (Pavulon), a medication that was used worldwide in anesthesiology as a non-depolarizing muscle relaxant at the time, in combination with propofol (Diprivan) to induce general anesthesia with longer acting muscle paralysis. Rocuronium is a nondepolarizing paralytic agent that induces muscle paralysis by competitive antagonism at the acetyl-cholinergic receptor.

Dosing of rocuronium can vary from 0.6–1.2 mg/kg. The onset of action is dose-dependent from 45–120 seconds, with a duration of action 30–90 minutes. Rocuronium is metabolized in the liver with a half-life of 1.4–2.4 hours.4

Cost Effectiveness

Currently, Rocuronium costs about $40 for a 100mg vial and is shelf stable for about 12 weeks, while Succinylcholine is about the same for a 200mg vial.  However, succinylcholine has a shelf life of only 2 weeks, which may result in higher departmental costs in the long-term. [5]

Winner: Rocuronium, due to a more stable shelf-life.

Faster Onset Time

A 65-year-old male with  with a history of alcoholic cirrhosis and known esophageal varices presents for hematemesis. The family states that he has had multiple episodes of vomiting over the past three hours. The patient is in obvious respiratory distress and begins to vomit again.

The decision is made to emergently intubate the patient and you prepare for RSI. Your nurse asks, “Do you want to use succinylcholine or rocuronium?” You reply, “Let’s use succinylcholine, it has a faster onset.” But does it?

Traditionally, succinylcholine is dosed 1–1.5 mg/kg and rocuronium is dosed 0.6–1.2 mg/kg. Succinylcholine generally takes 45–60 seconds for onset of laryngeal paralysis. When rocuronium is dosed at the lower end of this range, it’s onset of action is longer than the 45–60 seconds required for succinylcholine. However, if it’s dosed at the higher end of this range, at least 1.2 mg/kg, rocuronium’s onset of action is 45–60 seconds, just like succinylcholine.5

Winner: It’s a DRAW!

Fewest Side Effects or Contraindications

A 45-year-old female with recent burns to the lower extremities after being caught in a house fire four days ago presents to the ED for altered mental status and somnolence. The family states that they found her in her bedroom next to an empty bottle of vodka. The patient is tachycardic to the 120s with normal blood pressure, respiratory rate of 10, and an oxygen saturation of 93%. Her Glasgow coma scale is 7 and she presents with normal-sized but sluggish pupils. Given that she isn’t protecting her airway, you decide to RSI the patient. What’s your paralytic of choice for this patient?

Succinylcholine has been traditionally used as a first-line paralytic due to its quick onset of action and short half-life. Succinylcholine’s duration of action is 10–15 minutes, whereas the half-life of rocuronium is anywhere from 30–90 minutes, depending on the dose. However, succinylcholine has major side effects, including hyperkalemia, malignant hyperthermia, fasciculations and bradycardia. These effects are seen most significantly in patients with prior stroke, baseline neuromuscular disease and recent burn victims. Rocuronium has a much more limited side effect profile, and is limited to hepatotoxicity.5

Winner: Rocuronium

Safety Considerations

A 45-year-old male with an unknown medical history is found down on the sidewalk covered in a pool of vomitus and surrounded by his belongings. The patient appears disheveled with an unkempt beard, sluggish pupils of about 4 mm, heart rate in the 120s and a blood pressure of 100/60 mmHg. He’s breathing six times a minute with an oxygen saturation of 92% on room air.

You quickly decide that he needs to be intubated but want to be sure that he’s fully sedated and paralyzed in the hopes of reducing his risk of further aspiration. Which paralytic would you like to use?

Intubation conditions: A 2015 Cochrane review evaluated whether rocuronium could provide similar intubating conditions to succinylcholine for RSI. The review included results of a total of 50 trials, totaling > 4,000 patients. In general, succinylcholine was found to be superior to rocuronium when succinylcholine was dosed 1 mg/kg and rocuronium was dosed 0.6 mg/lg.6

When higher doses of rocuronium (1.2 mg/kg) were compared with succinylcholine, there was no difference between the two drugs in providing proper intubating conditions and first pass success rates.6

This review shows that rocuronium can be effectively used to provide proper intubating conditions in patients where succinylcholine is contraindicated. In addition, rocuronium has a significantly smaller side effect profile and may be a safer drug for RSI and induction for the general population.

Apnea time: Rocuronium has a 40-second longer safe apnea time when compared to succinylcholine. Safe apnea time is defined as the time required for a patient to clinically desaturate, with an SpO2 < 88% after paralysis.

The proposed mechanisms for succinylcholine’s decreased safe apnea time is due to the increased muscle oxygen consumption due to the associated fasciculations with succinylcholine. Multiple studies evaluate this topic and determined the fasciculation scores after injection of succinylcholine and rocuronium. Succinylcholine had significantly higher fasciculation scores than rocuronium. In addition, succinylcholine had higher levels of carbon dioxide three minutes after injection, further supporting the hypothesis that succinylcholine causes increased oxygen demand in muscles. An additional study found that succinylcholine also had a statistically significant increase in mean recovery time after apneic hypoxia compared to rocuronium.7,8

Duration of action: People say the biggest advantage to succinylcholine is a shorter duration of action. We all know that succinylcholine has a shorter duration of action than rocuronium; but is this really an advantage?

The safety of performing RSI lies within achieving the rapid induction of a paralytic state to decrease vocal cord movement and prevent stimulating the gag reflex of patients who have an unknown last oral intake to prevent aspiration. As EMS and emergency medicine providers, we don’t have the luxury of ensuring a fasting state to prevent aspiration like patients who are intubated in well-controlled operating room settings.

A patient who’s actively seizing or thrashing around in the back of an ambulance due to a hypoxic cerebral state increases the chance of further injury and decreased first-pass success rate.

Don’t we want our patients to be paralyzed? The prolonged paralysis achieved with rocuronium is actually an advantage to provide us more time to safely establish an airway, while decreasing the chances of aspiration and keeping people from waking up during a prolonged intubation. With adequate preparation and basic airway and ventilation skills, even if first-pass intubation isn’t successful, you should be able to bag a patient through an extended period paralysis or successfully place a supraglottic airway without the risk that the patient may aspirate or wake up in the middle of a procedure and self-extubate.

Winner: Rocuronium.

Chance of First-Pass Success

Recently, a new National Emergency Airway Registry (NEAR) series study was published in Annals of Emergency Medicine to finally settle this ongoing debate of which drug leads to the most amount of first-pass success (FPS)—our benchmark for a successful airway—with the least amount of adverse events. A large multicenter prospective trial was performed across 22 EDs to determine first-pass success rates between succinylcholine and rocuronium in patients > 14 years old over a one-year period. Adverse events were also compared between the two groups and subgroup analyses were performed based on weight-based dosages of the group.

Comparing 4,075 intubations across these EDs over a one-year period, no significant difference was noted (87.0% FPS with succinylcholine vs 87.5% FPS with rocuronium).  The incidence of adverse events was even more similar – 14.7% in the succinylcholine group vs 14.8% in the rocuronium group.  Overall, no difference was found in first-pass RSI success or peri-intubation adverse events in this large study. [9]

Winner: It’s a DRAW!

Overall Winner: Rocuronium

Both contenders were evenly matched and put up a strong fight in the ring, but rocuronium definitely edges out succinylcholine. When rocuronium is dosed appropriately, both drugs will get the job done, but rocuronium performs with more style, having less side effects and contraindications to consider when choosing a paralytic agent. Rocuronium also provides a safer apnea time, and a longer duration of paralysis which is a huge advantage to decreasing the possibility of aspiration.

Beyond the Paralytic Battle

More importantly, we may be looking in the wrong place for answers as to what truly make a difference to a successful and safer RSI. The more important question may not be paralytic choice, but instead, are we completely optimizing our patients for success using pre-oxygenation, proper patient positioning and peep valves for BVM?

But let’s look back and summarize our findings:

  1. Rocuronium is equivalent to succinylcholine in achieving intubating conditions and onset of action when dosed appropriately. When using rocuronium, give big doses of at least 1.2 mg/kg;
  2. Succinylcholine has many more contraindications and has a more extensive side effect profile than rocuronium, including significant hyperkalemia which could lead to deadly arrhythmias;
  3. Rocuronium has a much longer duration of action than succinylcholine, approximately 90 minutes, so be sure to properly sedate your patients until the paralytics wear off; and
  4. First-pass success isn’t significantly determined by paralytic choice. Instead, your focus should be on optimizing your patient prior to intubation and having multiple airway adjuncts, diverse methodologies for laryngoscopy and multiple backups to obtain airway if the first pass is unsuccessful.

References

1. Wallace C, McGuire B. Rapid sequence induction: Its place in modern anaesthesia. Continuing Education in Anaesthesia Critical Care & Pain. 2014;14(3):130–135.

2. Raghavendra T. Neuromuscular blocking drugs: Discovery and development. J R Soc Med. 2002;95(7):363–367.

3. Succinylcholine pathway, pharmacokinetics/pharmacodynamics. (Nov. 17, 2015.) PharmGKB. Retrieved May 13, 2019, from www.pharmgkb.org/pathway/PA166122732/overview.

4. Wicks TC. The pharmacology of rocuronium bromide (ORG 9426). AANA J. 1994;62(1):33–38.

5. Nickson C. (March 17, 2019.) Does Roc rock? Does Sux suck? Life in the Fast Lane.  Retrieved May 13, 2019, from www.litfl.com/does-roc-rock-does-sux-suck/.

6. Tran DTT, Newton EK, Mount VAH, et al. Rocuronium vs. succinylcholine for rapid sequence intubation: A Cochrane systematic review. Anaesthesia. 2014;72(6):765–777.

7. Tang L, Li S, Huang S, et al. Desaturation following rapid sequence induction using succinylcholine vs. rocuronium in overweight patients. Acta Anaesthesiol Scand. 2011;55(2):203-208.

8. Taha SK, El-Khatib MF, Baraka AS, et al. Effect of suxamethonium vs rocuronium on onset of oxygen desaturation during apnoea following rapid sequence induction. Anaesthesia. 2010;65(4):358–361

9. April MD, Arana A, Pallin DJ, et al. Emergency department intubation success with succinylcholine versus rocuronium: A National Emergency Airway Registry study. Ann Emerg Med. 2018;72(6):645–653.